Process for the preparation of 2,3,3,3-tetrafluoropropene

ABSTRACT

The invention provides a process for the preparation of 2,3,3,3-tetrafluoropropene (1234yf) comprising (a) contacting 1,1,1-trifluoro-2,3-difluoropropane (243db) with hydrogen fluoride (HF) in the presence of a zinc/chromia catalyst to produce a compound having the formula CF 3 CHFCH 2 X, wherein X is Cl or F, and (b) dehydrohalogenating the compound of formula CF 3 CHFCH 2 X to produce 1234yf.

The invention relates to a process for preparing2,3,3,3-tetrafluoropropene. In particular, the invention relates to aprocess for preparing 2,3,3,3-tetrafluoropropene comprising fluorinating1,1,1-trifluoro-2,3-dichloropropane and dehydrohalogenating a compoundformed from the fluorination to produce 2,3,3,3-tetrafluoropropene.

2,3,3,3-tetrafluoropropene is also known as HFO-1234yf, HFC-1234yf orsimply 1234yf. Hereinafter, unless otherwise stated,2,3,3,3-tetrafluoropropene will be referred to as 1234yf. The knownprocesses for preparing 1234yf typically suffer from disadvantages suchas low yields, and/or the handling of toxic and/or expensive reagents,and/or the use of extreme conditions, and/or the production of toxicby-products. Methods for the preparation of 1234yf have been describedin, for example, Journal Fluorine Chemistry (82), 1997, 171-174. In thispaper, 1234yf is prepared by the reaction of sulphur tetrafluoride withtrifluoroacetylacetone. However, this method is only of academicinterest because of the hazards involved in handling the reagents andtheir expense. Another method for the preparation of 1234yf is describedin U.S. Pat. No. 2,931,840. In this case, pyrolysis of C1chlorofluorocarbons with or without tetrafluoroethylene was purported toyield 1234yf. However, the yields described were very low and again itwas necessary to handle hazardous chemicals under extreme conditions. Itwould also be expected that such a process would produce a variety ofvery toxic by-products. In addition to addressing the disadvantages ofthe known methods, it would be desirable to provide a new method for thepreparation of 1234yf that use only readily available feedstocks.

The listing or discussion of a prior-published document in thisspecification should not necessarily be taken as an acknowledgement thatthe document is part of the state of the art or is common generalknowledge.

The present invention addresses the foregoing deficiencies of the knownroutes for preparing 1234yf by providing a process for its preparationcomprising (a) contacting 1,1,1-trifluoro-2,3-dichloropropane withhydrogen fluoride (HF) in the presence of a zinc/chromia catalyst toproduce a compound having the formula CF₃CHFCH₂X, wherein X is Cl or F;and (b) dehydrohalogenating the compound of formula CF₃CHFCH₂X toproduce 1234yf.

1,1,1-trifluoro-2,3-dichloropropane is also known as HCFC-243db orsimply 243db. Hereinafter, unless otherwise stated,1,1,1-trifluoro-2,3-dichloropropane will be referred to as 243db. Forthe avoidance of doubt, a compound of formula CF₃CHFCH₂X (wherein X═Clor F) may be either 1,1,1,2,3-pentafluoropropane (X═F, also known as HFC245eb or just 245eb) or 1,1,1,2-tetrafluoro-3-chloropropane (X═Cl, alsoknown as HFC 244eb or just 244eb), or a combination thereof.

Unless otherwise stated, as used herein, by the term“dehydrohalogenation” (or dehydrohalogenating), we refer to the removalof hydrogen chloride (HCl) or hydrogen fluoride (HF) from the compoundof formula CF₃CHFCH₂X. Thus the term “dehydrohalogenation” includes“dehydrofluorination” and “dehydrochlorination” of the compound offormula CF₃CHFCH₂X.

Step (a) of the process of the invention comprises contacting 243db withHF in the presence of a zinc/chromia catalyst to produce a compoundhaving the formula CF₃CHFCH₂X, i.e. step (a) is a fluorination step. Thefluorination may be carried out in the vapour and/or liquid phase and ata temperature of from about −70 to about 400° C. The process may becarried out at atmospheric, sub- or super-atmospheric pressure,preferably from about 0 to about 30 bara.

The catalyst in step (a) may be used in an amount of from about 0.01 toabout 50% by weight, such as from about 0.1 to about 30%, for examplefrom about 0.5 to about 20%, based on the combined weight of 243db andHF.

Step (b) of the process of the invention may be carried out by anysuitable reactions conditions effective to dehydrohalogenate (i.e.dehydrochlorinate or dehydrofluorinate) the compound of formulaCF₃CHFCH₂X to produce 1234yf. Preferably, the dehydrohalogenation iscarried out in the vapour and/or liquid phase and may be carried out ata temperature of from about −70 to about 1000° C. (e.g. about 0 to about400° C.). The process may be carried out at atmospheric sub- or superatmospheric pressure, preferably from about 0 to about 30 bara.

The dehydrohalogenation may be induced thermally, may be base-mediatedand/or may be catalysed by any suitable catalyst. Suitable catalystsinclude metal and carbon based catalysts such as those comprisingactivated carbon, main group (e.g. alumina-based catalysts) andtransition metals, such as chromia-based catalysts (e.g. zinc/chromia)or nickel-based catalysts (e.g. nickel mesh).

One preferred method of effecting the dehydrohalogenation of thecompound of formula CF₃CHFCH₂X to produce 1234yf is by contactingCF₃CHFCH₂X with a metal catalyst, such as a chromia-based (e.g.zinc/chromia) catalyst. Thus, steps (a) and (b) may be carried out in a“one-pot” manner, i.e. simultaneously. Alternatively, when both steps(a) and (b) are carried out in the presence of a metal catalyst, such asa chromia-based (e.g. zinc/chromia) catalyst, the fluorination anddehydrohalogenation reactions may be carried out in two discrete steps,for example using two or more discrete reaction zones or vessels.

Step (a) and/or step (b) can be carried out in any suitable apparatus,such as a static mixer, a stirred tank reactor or a stirredvapour-liquid disengagement vessel. Preferably, this or any otherapparatus described herein is made from one or more materials that areresistant to corrosion, e.g. Hastelloy® or Inconel®. The process may becarried out batch-wise or continuously.

When both steps (a) and (b) are carried out in the presence of azinc/chromia catalyst, the reaction conditions for each step (a) and (b)may be the same (e.g. in a one-pot process) or different. Preferably,the reaction conditions when steps (a) and (b) are carried out in thepresence of a zinc/chromia catalyst can be selected to be different soas to optimise the fluorination and dehydrohalogenation reactions,respectively. This is explained in more detail below.

Fluorination step (a) preferably is conducted at a temperature of fromabout 0 to about 390° C., such as from about 100 to about 380° C. orfrom about 200 to about 370° C. (e.g. from about 240 to about 260° C.).When conducted in the presence of a zinc/chromia catalyst, step (b)preferably is conducted at a temperature of from about 200 to about 360°C., such as from about 240 to about 340° C.

It is currently considered to be advantageous to use a higher pressurein step (a) (to promote fluorination) than in step (b) (to promotedehydrohalogenation). Thus, step (a) preferably is carried out fromabout 5 to about 28 bara, such as from about 10 to about 25 bara (e.g.15 to 20 bara), whereas step (b) preferably is carried out from about0.01 to about 25 bara or about 0.1 to about 20 bara, such as from about1 to about 10 bara (e.g. 1 to 5 bara).

Fluorination step (a) of the invention is carried out by contacting243db with HF. Step (b) of the invention may be carried out in thepresence of HF. For example residual HF from step (a) may be present,and/or HF from a separate feed. Alternatively, step (b) may be carriedout in the absence of HF, for example following separation of thecompound of formula CF₃CHFCH₂X from HF prior to step (b), and with noadditional co-feed of HF. In certain embodiments it may be desirable touse some HF in order to prevent and/or retard excessive decomposition ofthe organic feed and/or coking of the catalyst in step (b).

When both steps (a) and (b) are carried out in the presence of azinc/chromia catalyst and HF, the molar ratio of HF:organics can beselected to be different in each step so as to promote fluorination instep (a) and dehydrohalogenation in step (b). For example, the molarratio of HF:organics (e.g. 243db) in step (a) preferably is from about1:1 to about 100:1, such as from about 2:1 to about 50:1, for examplefrom about 5:1 to about 40:1 (e.g. from about 10:1 to about 30:1). Forstep (b), the molar ratio of HF:organics (e.g. the compound of formulaCF₃CHFCH₂X) preferably is from about 0.01:1 to about 50:1, such as fromabout 0.1:1 to about 40:1, for example from about 0.5:1 to about 30:1 orabout 2:1 to about 15:1 (e.g. from about 10:1 to about 20:1 or fromabout 5:1 to about 10:1).

Another way of increasing the concentration of HF in step (a) relativeto step (b) (thereby facilitating the fluorination/dehydrohalogenationreactions in these steps) is by adding a diluent gas (e.g. nitrogen) tostep (b).

Another preferred method of effecting the dehydrohalogenation of thecompound of formula CF₃CHFCH₂X to produce 1234yf is by contactingCF₃CHFCH₂X with a base (base-mediated dehydrohalogenation).

This base-mediated dehydrohalogenation process of step (b) comprisescontacting the CF₃CHFCH₂X with base such as a metal hydroxide or amide(preferably a basic metal hydroxide or amide, e.g. an alkali or alkalineearth metal hydroxide or amide).

Unless otherwise stated, as used herein, by the term “alkali metalhydroxide”, we refer to a compound or mixture of compounds selected fromlithium hydroxide, sodium hydroxide, potassium hydroxide, rubidiumhydroxide and caesium hydroxide. Similarly, by the term “alkali metalamide”, we refer to a compound or mixture of compounds selected fromlithium amide, sodium amide, potassium amide, rubidium amide and caesiumamide.

Unless otherwise stated, as used herein, by the term “alkaline earthmetal hydroxide”, we refer to a compound or mixture of compoundsselected from beryllium hydroxide, magnesium hydroxide, calciumhydroxide, strontium hydroxide and barium hydroxide. Similarly, by theterm “alkaline earth metal amide”, we refer to a compound or mixture ofcompounds selected from beryllium amide, magnesium amide, calcium amide,strontium amide and barium amide.

Typically, the base-mediated dehydrohalogenation process of step (b) isconducted at a temperature of from −50 to 300° C. Preferably, theprocess is conducted at a temperature of from 20 to 250° C., for examplefrom 50 to 200° C. The base-mediated dehydrohalogenation may beconducted at a pressure of from 0 to 30 bara.

The reaction time for the base-mediated dehydrohalogenation process ofstep (b) may vary over a wide range. However, the reaction time willtypically be in the region of from 0.01 to 100 hours, such as from 0.1to 50 hours, e.g. from 1 to 20 hours.

Of course, the skilled person will appreciate that the preferredconditions (e.g. temperature, pressure and reaction time) for conductingthe base-mediated dehydrohalogenation may vary depending on a number offactors such as the nature of the compound of formula CF₃CHFCH₂X, thebase being employed, and/or the presence of a catalyst etc.

The base-mediated dehydrohalogenation process of step (b) may be carriedout in the presence or absence of a solvent. If no solvent is used, thecompound of formula CF₃CHFCH₂X may be passed into or over molten base orhot base, for example in a tubular reactor. If a solvent is used, insome embodiments a preferred solvent is water, although many othersolvents may be used. In some embodiments solvents such as alcohols(e.g. propan-1-ol), diols (e.g. ethylene glycol) and polyols such aspolyethylene glycol (e.g. PEG200 or PEG300) may be preferred. Thesesolvents can be used alone or in combination. In further embodiments,solvents from the class known as polar aprotic solvents may bepreferred. Examples, of such polar aprotic solvents include diglyme,sulfolane, dimethylformamide (DMF), dioxane, acetonitrile,hexamethylphosphoramide (HMPA), dimethyl sulphoxide (DMSO) and N-methylpyrrolidone (NMP). The boiling point of the solvent is preferably suchthat it does not generate excessive pressure under reaction conditions.

A preferred base is an alkali metal hydroxide selected from the groupconsisting of lithium hydroxide, sodium hydroxide and potassiumhydroxide, more preferably, sodium hydroxide and potassium hydroxide andmost preferably potassium hydroxide.

Another preferred base is an alkaline earth metal hydroxide selectedfrom the group consisting of magnesium hydroxide and calcium hydroxide,more preferably calcium hydroxide.

The base is typically present in an amount of from 1 to 50 weight %based on the total weight of the components which make up step (b).Preferably, the base is present in an amount of from 5 to 30 weight %.

The molar ratio of base to compound of formula CF₃CHFCH₂X is typicallyfrom 1:20 to 50:1, preferably from 1:5 to 20:1, for example from 1:2 to10:1.

As mentioned above, the base-mediated dehydrohalogenation may preferablyemploy water as the solvent. Thus, the dehydrohalogenation reaction maypreferably use an aqueous solution of at least one base, such as analkali (or alkaline earth) metal hydroxide, without the need for aco-solvent or diluent. However, a co-solvent or diluent can be used forexample to modify the system viscosity, to act as a preferred phase forreaction by-products, or to increase thermal mass. Useful co-solvents ordiluents include those that are not reactive with or negatively impactthe equilibrium or kinetics of the process and include alcohols such asmethanol and ethanol; diols such as ethylene glycol; ethers such asdiethyl ether, dibutyl ether; esters such as methyl acetate, ethylacetate and the like; linear, branched and cyclic alkanes such ascyclohexane, methylcyclohexane; fluorinated diluents such ashexafluoroisopropanol, perfluorotetrahydrofuran and perfluorodecalin.

The base-mediated dehydrohalogenation of step (b) is preferablyconducted in the presence of a catalyst. The catalyst is preferably aphase transfer catalyst which facilitates the transfer of ioniccompounds into an organic phase from, for example, a water phase. Ifwater is used as a solvent, an aqueous or inorganic phase is present asa consequence of the alkali metal hydroxide and an organic phase ispresent as a result of the fluorocarbon. The phase transfer catalystfacilitates the reaction of these dissimilar components. While variousphase transfer catalysts may function in different ways, their mechanismof action is not determinative of their utility in the present inventionprovided that they facilitate the dehydrohalogenation reaction. Thephase transfer catalyst can be ionic or neutral and is typicallyselected from the group consisting of crown ethers, onium salts,cryptands and polyalkylene glycols and derivatives thereof (e.g.fluorinated derivatives thereof).

An effective amount of the phase transfer catalyst should be used inorder to effect the desired reaction, influence selectivity to thedesired products or enhance the yield; such an amount can be determinedby limited experimentation once the reactants, process conditions andphase transfer catalyst are selected. Typically, the amount of catalystused relative to the amount of compound of formula CF₃CHFCH₂X present isfrom 0.001 to 20 mol %, such as from 0.01 to 10 mol %, e.g. from 0.05 to5 mol %.

Crown ethers are cyclic molecules in which ether groups are connected bydimethylene linkages. Crown ethers form a molecular structure that isbelieved to be capable of receiving or holding the alkali metal ion ofthe hydroxide and to thereby facilitate the reaction. Particularlyuseful crown ethers include 18-crown-6 (especially in combination withpotassium hydroxide), 15-crown-5 (especially in combination with sodiumhydroxide) and 12-crown-4 (especially in combination with lithiumhydroxide).

Derivatives of the above crown ethers are also useful, such asdibenzyl-18-crown-6, dicyclohexanyl-18-crown-6, dibenzyl-24-crown-8 anddibenzyl-12-crown-4. Other compounds analogous to the crown ethers anduseful for the same purpose are compounds which differ by thereplacement of one or more of the oxygen atoms by other kinds of donoratoms, particularly N or S. Fluorinated derivatives of all the above mayalso be used.

Cryptands are another class of compounds useful in the base-mediateddehydrohalogenation as phase transfer catalysts. These are threedimensional polymacrocyclic chelating agents that are formed by joiningbridgehead structures with chains that contain properly spaced donoratoms. The donor atoms of the bridges may all be O, N, or S, or thecompounds may be mixed donor macrocycles in which the bridge strandscontain combinations of such donor atoms. Suitable cryptands includebicyclic molecules that result from joining nitrogen bridgeheads withchains of (—OCH₂CH₂—) groups, for example as in [2.2.2]cryptand(4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, availableunder the brand names Kryptand 222 and Kryptofix 222).

Onium salts that may be used as catalysts in the base-mediated processof the step (b) include quaternary phosphonium salts and quaternaryammonium salts, which may be represented by the formulae R¹R²R³R⁴P⁺Z⁻and R¹R²R³R⁴N⁺Z⁻, respectively. In these formulae, each of R¹, R², R³and R⁴ typically represent, independently, a C₁₋₁₀ alkyl group, an arylgroup (e.g. phenyl, naphthyl or pyridinyl) or an arylalkyl group (e.g.benzyl or C₁₋₁₀ alkyl-substituted phenyl), and Z⁻ is a halide or othersuitable counterion (e.g. hydrogen sulphate).

Specific examples of such phosphonium salts and quaternary ammoniumsalts include tetramethylammonium chloride, tetramethylammonium bromide,benzyltriethylammonium chloride, methyltrioctylammonium chloride(available commercially under the brands Aliquat 336 and Adogen 464),tetra-n-butylammonium chloride, tetra-n-butylammonium bromide,tetra-n-butylammonium hydrogen sulphate, tetra-n-butylphosphoniumchloride, tetraphenylphosphonium bromide, tetraphenylphosphoniumchloride, triphenylmethylphosphonium bromide andtriphenylmethylphosphonium chloride. Benzyltriethylammonium chloride ispreferred for use under strongly basic conditions.

Other useful onium salts include those exhibiting high temperaturestabilities (e.g. up to about 200° C.), for example4-dialkylaminopyridinium salts, tetraphenylarsonium chloride,bis[tris(dimethylamino)phosphine]iminium chloride andtetrakis[tris(dimethylamino)phosphinimino]phosphonium chloride. Thelatter two compounds are also reported to be stable in the presence ofhot, concentrated sodium hydroxide and, therefore, can be particularlyuseful.

Polyalkylene glycol compounds useful as phase transfer catalysts may berepresented by the formula R⁶O(R⁵O)_(m)R⁷ wherein R⁵ is a C₁₋₁₀ alkylenegroup, each of R⁶ and R⁷ are, independently H, a C₁₋₁₀ alkyl group, anaryl group (e.g. phenyl, naphthyl or pyridinyl) or an arylalkyl group(e.g. benzyl or C₁₋₁₀ alkyl-substituted phenyl), and m is an integer ofat least 2. Preferable both R⁶ and R⁷ are the same, for example they mayboth by H.

Such polyalkylene glycols include diethylene glycol, triethylene glycol,tetraethylene glycol, pentaethylene glycol, hexaethylene glycol,diisopropylene glycol, dipropylene glycol, tripropylene glycol,tetrapropylene glycol and tetramethylene glycol, monoalkyl glycol etherssuch as monomethyl, monoethyl, monopropyl and monobutyl ethers of suchglycols, dialkyl ethers such as tetraethylene glycol dimethyl ether andpentaethylene glycol dimethyl ether, phenyl ethers, benzyl ethers ofsuch glycols, and polyalkylene glycols such as polyethylene glycol(average molecular weight about 300) and polyethylene glycol (averagemolecular weight about 400) and the dialkyl (e.g. dimethyl, dipropyl,dibutyl)ethers of such polyalkylene glycols.

Combinations of phase transfer catalysts from within one of the groupsdescribed above may also be useful as well as combinations or mixturesfrom more than one group. Crown ethers and quaternary ammonium salts arethe currently preferred groups of catalysts, for example 18-crown-6 andits fluorinated derivatives and benzyltriethylammonium chloride.

By the term “zinc/chromia catalyst” we mean any catalyst comprisingchromium or a compound of chromium and zinc or a compound of zinc. Suchcatalysts are known in the art, see for example EP-A-0502605,EP-A-0773061, EP-A-0957074 and WO 98/10862, which are incorporated byreference herein. However, the present inventors have surprisingly foundthat zinc/chromia catalysts may be used promote the fluorination of243db to produce the compound of formula CF₃CHFCH₂X and, optionally, topromote the dehydrohalogenation of the compound of formula CF₃CHFCH₂X toproduce 1234yf. The combined fluorination/dehydrohalogenation to produce1234yf starting from 243db in the presence of a zinc/chromia catalyst isparticularly unexpected.

Typically, the chromium or compound of chromium present in thezinc/chromia catalysts of the invention is an oxide, oxyfluoride orfluoride of chromium such as chromium oxide.

The total amount of the zinc or a compound of zinc present in thezinc/chromia catalysts of the invention is typically from about 0.01% toabout 25%, preferably 0.1% to about 25%, conveniently 0.01% to 6% zinc,and in some embodiments preferably 0.5% by weight to about 25% by weightof the catalyst, preferably from about 1 to 10% by weight of thecatalyst, more preferably from about 2 to 8% by weight of the catalyst,for example about 4 to 6% by weight of the catalyst.

In other embodiments, the catalyst conveniently comprises 0.01% to 1%,more preferably 0.05% to 0.5% zinc.

The preferred amount depends upon a number of factors such as the natureof the chromium or a compound of chromium and/or zinc or a compound ofzinc and/or the way in which the catalyst is made. These factors aredescribed in more detail hereinafter.

It is to be understood that the amount of zinc or a compound of zincquoted herein refers to the amount of elemental zinc, whether present aselemental zinc or as a compound of zinc.

The zinc/chromia catalysts used in the invention may include anadditional metal or compound thereof. Typically, the additional metal isa divalent or trivalent metal, preferably selected from nickel,magnesium, aluminium and mixtures thereof. Typically, the additionalmetal is present in an amount of from 0.01% by weight to about 25% byweight of the catalyst, preferably from about 0.01 to 10% by weight ofthe catalyst. Other embodiments may comprise at least about 0.5% byweight or at least about 1% weight of additional metal.

The zinc/chromia catalysts used in the present invention may beamorphous. By this we mean that the catalyst does not demonstratesubstantial crystalline characteristics when analysed by, for example,X-ray diffraction.

Alternatively, the catalysts may be partially crystalline. By this wemean that from 0.1 to 50% by weight of the catalyst is in the form ofone or more crystalline compounds of chromium and/or one or morecrystalline compounds of zinc. If a partially crystalline catalyst isused, it preferably contains from 0.2 to 25% by weight, more preferablyfrom 0.3 to 10% by weight, still more preferably from 0.4 to 5% byweight of the catalyst in the form of one or more crystalline compoundsof chromium and/or one or more crystalline compounds of zinc.

During use in a fluorination/dehydrohalogenation reaction the degree ofcrystallinity may change. Thus it is possible that a catalyst of theinvention that has a degree of crystallinity as defined above before usein a fluorination/dehydrohalogenation reaction and will have a degree ofcrystallinity outside these ranges during or after use in afluorination/dehydrohalogenation reaction.

The percentage of crystalline material in the catalysts of the inventioncan be determined by any suitable method known in the art. Suitablemethods include X-ray diffraction (XRD) techniques. When X-raydiffraction is used the amount of crystalline material such as theamount of crystalline chromium oxide can be determined with reference toa known amount of graphite present in the catalyst (eg the graphite usedin producing catalyst pellets) or more preferably by comparison of theintensity of the XRD patterns of the sample materials with referencematerials prepared from suitable internationally recognised standards,for example NIST (National Institute of Standards and Technology)reference materials.

The zinc/chromia catalysts of the invention typically have a surfacearea of at least 50 m²/g and preferably from 70 to 250 m²/g and mostpreferably from 100 to 200 m²/g before it is subjected to pre-treatmentwith a fluoride containing species such as hydrogen fluoride or afluorinated hydrocarbon. During this pre-treatment, which is describedin more detail hereinafter, at least some of the oxygen atoms in thecatalyst are replaced by fluorine atoms.

The zinc/chromia catalysts of the invention typically have anadvantageous balance of levels of activity and selectivity. Preferably,they also have a degree of chemical robustness that means that they havea relatively long working lifetime. The catalysts of the inventionpreferably also have a mechanical strength that enables relatively easyhandling, for example they may be charged to reactors or discharged fromreactors using known techniques.

The zinc/chromia catalysts of the invention may be provided in anysuitable form known in the art. For example, they may be provided in theform of pellets or granules of appropriate size for use in a fixed bedor a fluidised bed. The catalysts may be supported or unsupported. Ifthe catalyst is supported, suitable supports include AlF₃, fluorinatedalumina or activated carbon.

The zinc/chromia catalysts of the invention include promoted forms ofsuch catalysts, including those containing enhanced Lewis and/orBrönsted acidity and/or basicity.

The amorphous catalysts which may be used in the present invention canbe obtained by any method known in the art for producing amorphouschromia-based catalysts. Suitable methods include co-precipitation fromsolutions of zinc and chromium nitrates on the addition of ammoniumhydroxide. Alternatively, surface impregnation of the zinc or a compoundthereof onto an amorphous chromia catalyst can be used.

Further methods for preparing the amorphous zinc/chromia catalystsinclude, for example, reduction of a chromium (VI) compound, for examplea chromate, dichromate, in particular ammonium dichromate, to chromium(III), by zinc metal, followed by co-precipitation and washing; ormixing as solids, a chromium (VI) compound and a compound of zinc, forexample zinc acetate or zinc oxalate, and heating the mixture to hightemperature in order to effect reduction of the chromium (VI) compoundto chromium (III) oxide and oxidise the compound of zinc to zinc oxide.

The zinc may be introduced into and/or onto the amorphous chromiacatalyst in the form of a compound, for example a halide, oxyhalide,oxide or hydroxide depending at least to some extent upon the catalystpreparation technique employed. In the case where amorphous catalystpreparation is by impregnation of a chromia, halogenated chromia orchromium oxyhalide, the compound is preferably a water-soluble salt, forexample a halide, nitrate or carbonate, and is employed as an aqueoussolution or slurry. Alternatively, the hydroxides of zinc and chromiummay be co-precipitated (for example by the use of a base such as sodiumhydroxide or ammonium hydroxide) and then converted to the oxides toprepare the amorphous catalyst. Mixing and milling of an insoluble zinccompound with the basic chromia catalyst provides a further method ofpreparing the amorphous catalyst precursor. A method for makingamorphous catalyst based on chromium oxyhalide comprises adding acompound of zinc to hydrated chromium halide.

The amount of zinc or a compound of zinc introduced to the amorphouscatalyst precursor depends upon the preparation method employed. It isbelieved that the working catalyst has a surface containing cations ofzinc located in a chromium-containing lattice, for example chromiumoxide, oxyhalide, or halide lattice. Thus the amount of zinc or acompound of zinc required is generally lower for catalysts made byimpregnation than for catalysts made by other methods such asco-precipitation, which also contain the zinc or a compound of zinc innon-surface locations.

Any of the aforementioned methods, or other methods, may be employed forthe preparation of the amorphous catalysts which may be used in theprocess of the present invention.

The zinc/chromia catalysts described herein are typically stabilised byheat treatment before use such that they are stable under theenvironmental conditions that they are exposed to in use. Thisstabilisation is often a two-stage process. In the first stage, thecatalyst is stabilised by heat treatment in nitrogen or a nitrogen/airenvironment. In the art, this stage is often called “calcination”.Fluorination catalysts are then typically stabilised to hydrogenfluoride by heat treatment in hydrogen fluoride. This stage is oftentermed “pre-fluorination”.

By careful control of the conditions under which these two heattreatment stages are conducted, crystallinity can be induced into thecatalyst to a controlled degree.

For example, an amorphous catalyst may be heat treated at a temperatureof from about 300 to about 600° C., preferably from about 400 to 600°C., more preferably from 500 to 590° C., for example 520, 540, 560 or580° C. for a period of from about 1 to about 12 hours, preferably forfrom about 2 to about 8 hours, for example about 4 hours in a suitableatmosphere. Suitable atmospheres under which this heat treatment can beconducted include an atmosphere of nitrogen or an atmosphere having anoxygen level of from about 0.1 to about 10% v/v in nitrogen. Otheroxidizing environments could alternatively be used. For example,environments containing suitable oxidizing agents include, but are notlimited to, those containing a source of nitrate, CrO₃ or O₂ (forexample air). This heat treatment stage can be conducted in addition toor instead of the calcining stage that is typically used in the priorart to produce amorphous catalysts.

Conditions for the pre-fluorination stage can be selected so that theydo not substantially introduce crystallinity into the catalyst. This maybe achieved by heat treatment of the catalyst precursor at a temperatureof from about 200 to about 500° C., preferably from about 250 to about400° C. at atmospheric or super atmospheric pressure for a period offrom about 1 to about 16 hours in the presence of hydrogen fluoride,optionally in the presence of another gas such as nitrogen.

Conditions for the pre-fluorination stage can be selected so that theyinduce a change in the crystallinity of the catalyst or so that they donot induce such a change. The present inventors have found that heattreatment of the catalyst precursor at a temperature of from about 250to about 500° C., preferably from about 300 to about 400° C. atatmospheric or super atmospheric pressure for a period of from about 1to about 16 hours in the presence of hydrogen fluoride, optionally inthe presence of another gas such as air, can produce a catalyst in whichthe crystallinity is as defined above, for example from 0.1 to 8.0% byweight of the catalyst (typically from 0.1 to less than 8.0% by weightof the catalyst) is in the form of one or more crystalline compounds ofchromium and/or one or more crystalline compounds of the at least oneadditional metal.

The skilled person will appreciate that by varying the conditionsdescribed above, such as by varying the temperature and/or time and/oratmosphere under which the heat treatment is conducted, the degree ofcrystallinity of the catalyst may be varied. Typically, for example,catalysts with higher degrees of crystallinity (e.g. from 8 to 50% byweight of the catalyst) may be prepared by increasing the temperatureand/or increasing the calcination time and/or increasing the oxidisingnature of the atmosphere under which the catalyst pre-treatment isconducted.

The variation of catalyst crystallinity as a function of calcinationtemperature, time and atmosphere is illustrated by the following tableshowing a series of experiments in which 8 g samples of a 6%zinc/chromia catalyst were subjected to calcination across a range ofconditions and the level of crystallinity induced determined by X-Raydiffraction.

Calcination Calcination Atmosphere % Cryst Time Temperature nitrogen:airCr₂O₃ (t, hrs) (T, ° C.) (D, v/v) Content 4 400.0 15 1 4 400.0 15 1 2450.0 20 9 6 350.0 20 0 2 450.0 10 18 2 350.0 10 0 6 450.0 20 20 6 350.010 0 6 450.0 10 30 4 400.0 15 1 2 350.0 20 0

The pre-fluorination treatment typically has the effect of lowering thesurface area of the catalyst. After the pre-fluorination treatment thecatalysts of the invention typically have a surface area of 20 to 200m²/g, such as 50 to 150 m²/g, for example less than about 100 m²/g.

In use, the zinc/chromia catalyst may be regenerated or reactivatedperiodically by heating in air at a temperature of from about 300° C. toabout 500° C. Air may be used as a mixture with an inert gas such asnitrogen or with hydrogen fluoride, which emerges hot from the catalysttreatment process and may be used directly in fluorination processesemploying the reactivated catalyst. Alternatively, the catalyst can beregenerated continuously whilst in use by introducing an oxidising gasinto the reactor e.g. oxygen or chlorine.

1,1,1-trifluoro-2,3-dichloropropane (243db) is commercially available(e.g. from Apollo Scientific Ltd, UK). Alternatively, 243db may also beprepared via a synthetic route starting from the cheap feedstocks carbontetrachloride (CCl₄) and ethylene (see the reaction scheme set outbelow). These two starting materials may be telomerised to produce1,1,1,3-tetrachloropropane (see, for example, J. Am. Chem. Soc. Vol. 70,p 2529, 1948, which is incorporated herein by reference) (also known asHCC-250fb, or simply 250fb).

250fb may then be fluorinated to produce 3,3,3-trifluoropropene (1243zf)and/or 1,1,1-trifluoro-3-chloropropane (e.g. using HF, optionally in thepresence of a chromia-containing catalyst, preferably a zinc/chromiacatalyst as described herein). Dehydrohalogenation of1,1,1-trifluoro-3-chloropropane (e.g. using NaOH or KOH) produces3,3,3-trifluoropropene (1243zf). Alternatively, 250fb may bedehydrochlorinated to 3,3,3-trichloropropene, followed by fluorinationto 1243zf.

1243zf may then be readily halogenated, such as chlorinated (e.g. withchlorine) to produce 1,1,1-trifluoro-2,3-dichloropropane (243db). Thisreaction scheme is summarised below (minus the route from 250fb to1243zf via 3,3,3-trichloropropene).

Thus, in another aspect of the invention, there is provided a processfor preparing 1234yf, the process comprising:(i) telomerising ethylene and carbon tetrachloride (CCl₄) to produce1,1,1,3-tetrachloropropane (250fb);(ii) converting 250fb to 3,3,3-trifluoropropene (1243zf);(iii) contacting 1243zf with a compound of formula AB to produce acompound of formula CF₃CHACH₂B, wherein A and B represent,independently, H, F, Cl, Br or I, provided that A and B are not both Hor F;(iv) contacting the compound of formula CF₃CHACH₂B with hydrogenfluoride (HF) in the presence of a zinc/chromia catalyst to produce acompound having the formula CF₃CHFCH₂X, wherein X is Cl or F; and(v) dehydrohalogenating the compound of formula CF₃CHFCH₂X to produce1234yf.

Step (i) of the above process typically comprises contacting ethylenewith CCl₄ in the liquid and/or vapour phase in presence of a catalystunder conditions suitable to produce 250fb.

Any suitable catalyst may be used in step (i), such as a catalyst whichcomprises iron, copper and/or peroxide.

Catalysts which comprise peroxide include benzoyl peroxide anddi-t-butyl peroxide. Catalysts which comprise iron include iron powderand ferric/ferrous halides (e.g. chlorides). Catalysts which comprisecopper include salts of copper such as copper halides (e.g. CuCl₂),copper sulphate and/or copper cyanide.

Typically, the catalysts which comprise copper and iron are used with aco-catalyst or ligand. Suitable co-catalysts includetriethylorthoformate (HC(OEt)₃), nitrogen/phosphorus-containing ligands,and/or ammonium/phosphonium salts. Preferred nitrogen-containing ligandsinclude amines (e.g. primary and secondary amines), nitriles and amides.Preferred phosphorus containing ligands include phosphates, phosphites(e.g. triethylphosphite) and phosphines. Preferred ammonium andphosphonium salts include ammonium and phosphonium halides (e.g.chlorides).

The catalyst for step (i) typically is used in an amount from about 0.01to about 50 mol % (e.g. about 0.1 to about 10%), based on the molar sumof CCl₄ and ethylene present. An excess of the carbon tetrachloride overethylene generally is used. For example, the molar ratio of CCl₄:C₂H₄typically is from about 1:1 to about 50:1, such as from about 1.1:1 toabout 20:1, for example from about 1.2:1 to about 10:1 or about 1.5:1 toabout 5:1.

The reaction temperature for step (i) typically is within the range offrom about 20 to about 300° C., preferably from about 30 to about 250°C., such as from about 40 to about 200° C., e.g. from about 50 to about150° C.

The reaction pressure for step (i) typically is within the range of from0 to about 40 bara, preferably from about 1 to about 30 bara.

The reaction time for step (i) generally is from about 1 second to about100 hours, preferably from about 10 seconds to about 50 hours, such asfrom about 1 minute to about 10 hours.

Step (i) can be carried out in any suitable apparatus, such as a staticmixer, a tubular reactor, a stirred tank reactor or a stirredvapour-liquid disengagement vessel. Step (i) may be carried outbatch-wise or continuously. Preferably, the 1,1,1,3-tetrachloropropaneformed in step (i) is purified and/or isolated before it is fluorinatedin step (ii). The purification may be achieved by separation of the250fb from any other products or reagents by one or more distillation,condensation or phase separation steps and/or by scrubbing with water oraqueous base.

The conversion of 250fb to 1243zf in step (ii) above typically involvesfluorination and dehydrohalogenation sub-steps.

For example, 250fb may be fluorinated to produce a compound of formulaCF₃CH₂CH₂Cl (253fb), followed by dehydrohalogenation of 253fb to produce1243zf. This will be referred to hereinafter as route (ii1).

Alternatively, 250fb may be dehydrochlorinated to produce3,3,3-trichloropropene, followed by fluorination to produce 1243zf. Thiswill be referred to hereinafter as route (ii2).

Either or both routes (ii1) and (ii2) may be used to convert 250fb to1243zf, depending on the choice of reagents and/or catalysts. The routetaken and the number of steps involved may depend on factors such as thereaction conditions and the nature of catalyst employed (if any). Suchfactors are described in more detail below.

In route (ii1), for example, 250fb may be fluorinated with HF in thepresence of a catalyst to produce 253fb. Any suitable catalyst for HFfluorination may be used, such as compounds comprising aluminium (e.g.alumina-based catalysts) and/or chromium (e.g. chromia-based catalysts,especially zinc/chromia catalysts as described herein) and/or metalhalides such as chlorides or fluorides (e.g. TaX₅, SbX₅, SnX₄, TiX₄,FeCl₃, NbX₅, VX₅, AlX₃, wherein X═F or Cl) and/or nitrogen-containingbases (e.g. amines and nitrogen-containing heterocycles such aspyridine). Examples of catalysts compounds comprising aluminium includeAlF₃, optionally mixed with one or more transition metal compounds.

253fb may then be dehydrohalogenated to 1243zf by any suitable method,for example by base-mediated (e.g. using a base comprising alkali oralkaline earth metal hydroxides or amides), thermal or metal catalysed(e.g. zinc/chromia catalysed) dehydrohalogenation. Thedehydrohalogenation may be conducted in the presence or absence of HF.Suitable reaction conditions for the dehydrohalogenation of 253fb aredescribed hereinbefore in relation to the dehydrohalogenation step (b)of a compound of formula CF₃CHFCH₂X (wherein X═Cl or F).

The fluorination and dehydrohalogenation reactions in route (ii1) usingHF may be conducted simultaneously (i.e. in a one-pot process) orsequentially, optionally with separation/isolation of the 253fb prior todehydrohalogenation. Preferably, route (ii1) is carried out in one-potusing a zinc/chromia catalyst.

In route (ii2), the dehydrochlorination and fluorination reactions maybe carried out under substantially the same reaction conditions, i.e. ina one-pot process. Thus, 250fb may be contacted with HF in the presenceof a catalyst to produce 1243zf, typically via 253fb. Suitable catalystsinclude the catalysts described above in relation to route (ii1),particularly zinc/chromia catalysts.

Although HF is described as a suitable fluorination agent for step (ii),any suitable fluorination agent may be used. For example, in analternative embodiment, 3,3,3-trifluoropropene may be produced in onepot by treating 1,1,1,3-tetrachloropropane with NaF, KF, or amine:HFcomplexes such as Olah's reagent.

Typically, step (ii) is carried out at a temperature of about 20 toabout 500° C. For example, when using KF or Olah's reagent (pyrindiniumpoly(HF)), temperatures of about 50 to about 200° C. may be used.Alternatively, when using HF, higher temperatures may be employed, suchas from about 100 to about 500° C. (e.g. about 120 to about 400° C. orabout 150 to about 250° C.).

The temperature used may vary depending on the nature of the catalystemployed. For example, when a nitrogen-containing base is used, thepreferred temperature may range from about 100 to about 250° C., whereaswhen a catalyst based on a compound of aluminium is employed, thepreferred temperature may vary from about 200 to about 350° C. When azinc/chromia catalyst is used for step (ii), the temperature typicallyranges from about 150 to about 400° C., such as from about 150 to about350° C., e.g. from about 150 to about 300° C. or from about 150 to about250° C.

The reaction pressure for step (ii) typically is within the range offrom 0 to about 30 bara, preferably from about 1 to about 20 bara.

An excess of the fluorination agent is generally used in step (ii),whether the 3,3,3-trifluoropropene is produced via route (ii1) or route(ii2). For example, when using HF as the fluorination agent, a molarratio of HF:organics of from about 1:1 to about 100:1, such as fromabout 3:1 to about 50:1, e.g. from about 6:1 to about 30:1 may be used.

The reaction time for step (ii) generally is from about 1 second toabout 100 hours, preferably from about 10 seconds to about 50 hours,such as from about 1 minute to about 10 hours. In a continuous process,typical contact times of the catalyst with the reagents is from about 1to about 1000 seconds, such from about 1 to about 500 seconds or about 1to about 300 seconds or about 1 to about 50, 100 or 200 seconds.

Step (ii) can be carried out in any suitable apparatus, such as a staticmixer, a tubular reactor, a stirred tank reactor or a stirredvapour-liquid disengagement vessel. Step (ii) may be carried outbatch-wise or continuously. Preferably, the 1243zf formed in step (ii)is purified and/or isolated before it is reacted in step (iii). Thepurification may be achieved by separation of the 1243zf from any otherproducts or reagents by one or more distillation, condensation or phaseseparation steps and/or by scrubbing with water or aqueous base.

Step (ii) is described in more detail towards the end of thisspecification in a further embodiment denoted the 1243zf preparationprocess.

Step (iii) is the halogenation of 1243zf and comprises contacting 1243zfwith a compound of formula AB to produce a compound of formulaCF₃CHACH₂B, wherein A and B represent, independently, H, F, Cl, Br or I,provided that A and B are not both H or F. Any suitable halogenatingagent AB may be used in step (iii) to convert 1243zf to the compound offormula CF₃CHACH₂B. Examples include Cl₂, Br₂, I₂, ClF, ClBr, and ICl,each optionally in the presence of HF. Preferably, at least one of A orB is Cl and, therefore, 1243zf may be chlorinated by contacting it withCl₂, ClF, ClBr and/or ICl. Chlorine (Cl₂) is a preferred chlorinatingagent. Preferably, step (iii) is carried out by contacting 1243zf withchlorine (Cl₂) to produce 243db.

Step (iii) is advantageously carried out in the presence of a catalyst.Any suitable catalyst may be used, including catalysts comprising atransition metal (e.g. Ti, V, Cr, Mn, Fe, Co, Ni, Sn, Ta, Sb, Au, Ag,Mo, Ru, Rh, Pd, Pt or compounds thereof or mixtures of the foregoing) ora main group element such as carbon, silicon or aluminium or compoundsthereof or mixtures of the foregoing. A preferred group of chlorinationcatalysts are those comprising activated carbon, alumina and/or an oxideof a transition metal.

For the avoidance of doubt, by a catalyst which comprises activatedcarbon, alumina and/or an oxide of a transition metal, we includecatalysts that are essentially only activated carbon, alumina and/or anoxide of a transition metal and catalysts that are activated carbon,alumina and/or an oxide of a transition metal modified, for example, bythe addition of one or more metals (e.g. transition metals) and/orcompounds thereof.

By “activated carbon”, we include any carbon with a relatively highsurface area such as from about 50 to about 3000 m² or from about 100 toabout 2000 m² (e.g. from about 200 to about 1500 m² or about 300 toabout 1000 m²). The activated carbon may be derived from anycarbonaceous material, such as coal (e.g. charcoal), nutshells (e.g.coconut) and wood. Any form of activated carbon may be used, such aspowdered, granulated and pelleted activated. Activated carbon which hasbeen modified (e.g. impregnated) by the addition of Cr, Mn, Au, Fe, Sn,Ta, Ti, Sb, Al, Co, Ni, Mo, Ru, Rh, Pd and/or Pt and/or a compound (e.g.a halide) of one or more of these metals may be used.

Alumina which has been modified by the addition of Cr, Mn, Fe, Sn, Ta,Ti, Sb, Al, Co, Ni, Mo, Ru, Rh, Pd and/or Pt and/or a compound (e.g. ahalide) of one or more of these metals may be used.

An oxide of a transition metal that has been modified by the addition ofCr, Mn, Au, Fe, Sn, Ta, Ti, Sb, Al, Co, Ni, Mo, Ru, Rh, Pd and/or Ptand/or a compound (e.g. a halide) of one or more of these metals may beused.

A preferred oxide of a transition metal is an oxide of Cr, Ti, V, Zr, orFe. For example, chromia (Cr₂O₃) alone, or chromia that has beenmodified by the addition of Zn, Mn, Zr, Ni, Al and/or Mg and/or acompound of one or more of these metals may be used. Suitablechromia-based catalysts include those described in EP-A-0502605,EP-A-0773061, EP-A-957074, WO 98/10862 and WO 2006/106353. A preferredchromia-based catalyst is a zinc/chromia catalyst.

Activated carbon is currently a preferred catalyst for step (iii)because, for example, it is cheap, effective and robust. Activatedcarbon is commercially available, e.g. from Sutcliffe-Speakman.

Step (iii) may be conducted in the vapour or liquid phase, preferably inthe vapour phase. Step (iii) may be carried in the liquid phase usingthe 243db product as the solvent. The heat of reaction in such a processmay be removed by boiling off the 243db product/solvent.

Typically, step (iii) is conducted at a temperature of from about −100to about 400° C., such as from about −80 to about 300° C. or −50 toabout 250° C., e.g. from about 0 to about 200° C. or about 50 to about150° C. The process may be conducted at a pressure of from about 0 toabout 30 bara, such as from about 0.1 to about 20 bara or from about 0.5to about 10 bara, e.g. from about 1 to about 5 bara.

Step (iii) can be carried out in any suitable apparatus, such as astatic mixer, a tubular reactor, a stirred tank reactor or a stirredvapour-liquid disengagement vessel. Step (iii) may be carried outbatch-wise or continuously.

The reaction time for step (iii) generally is from about 1 second toabout 100 hours, preferably from about 10 seconds to about 50 hours,such as from about 1 minute to about 10 hours.

Typically, the molar ratio of 1243zf:compound of formula AB (e.g. Cl₂)in step (iii) is from about 10:1 to about 1:5, such as from about 5:1 toabout 1:2, for example from about 3:1 to about 1.5:1 (e.g. about 2.5:1to about 1:1).

The compound of formula CF₃CHACH₂B (e.g. 243db) formed in step (iii) maybe purified and/or isolated before being used in step (iv). For example,the compound of formula CF₃CHACH₂B may be separated (e.g. bydistillation, condensation and phase separation, and/or scrubbing withwater or aqueous base) from the compound of formula AB and 1243zf instep (iii) and transferred to a different reaction vessel or zone forconducting the fluorination step (iv).

In this way, the reaction conditions (e.g. temperature and pressure)used in step (iii) and (iv) can be optimised to facilitate thehalogenation and fluorination reactions, respectively. For example, itis currently thought to be optimal to use higher temperature and/orpressure conditions in the fluorination step (iv) compared to thehalogenation step (iii).

In another embodiment, step (iii) may be combined with step (iv), i.e.these steps may be carried out simultaneously in a one-pot process. Thiscombined process (referred to hereinafter as process (x)) comprisescontacting 3,3,3-trifluoropropene (1243zf) with a compound of formula ABselected from Cl₂, Br₂, I₂, ClF, ClBr, and ICl and HF in the presence ofa zinc/chromia catalyst to produce a compound of formula CF₃CHFCH₂X,wherein X is Cl or F. Thus, in process (x), the zinc/chromia catalystacts as both a chlorination and fluorination catalyst. Chlorine (Cl₂) isa preferred compound of formula AB in process (x).

In process (x), the conditions used (e.g. temperature, pressure andmolar ratio of 1243:chlorine) fall within the broadest ranges set outabove in relation to the halogenation of 1243zf to the compound offormula CF₃CHACH₂B (e.g. 243db) (i.e. step (iii) alone). However, thesimultaneous chlorination/hydrofluorination in process (x) may require ahigher temperature compared to the corresponding halogenation (e.g.chlorination) alone defined in step (iii). For example, preferredtemperature conditions for process (x) typically range from about 50 toabout 400° C., such as from about 100 to about 350° C.

Typically, HF will be used in a molar excess compared to the amount of1243zf and/or chlorine in process (x). For example, the molar ratio ofHF:1243zf may be in the range of from about 1:1 to about 200:1, such asfrom about 2:1 to about 150:1, e.g. from about 5:1 to about 100:1.

As described hereinbefore, steps (a) and (b) may be conducted in aone-pot process. Steps (a) and (b) correspond to steps (iv) and (v).Thus, steps (iii), (iv) and (v) may also be carried out simultaneously,and in a further aspect of the invention, there is provided a processfor preparing 1234yf comprising contacting 3,3,3-trifluoropropene(1243zf) with chlorine a compound of formula AB and HF in the presenceof a zinc/chromia catalyst to produce 1234yf, wherein A and B represent,independently, H, F, Cl, Br or I, provided that A and B are not both Hor F. This will be referred to hereinafter as process (y).

Any suitable halogenating agent of formula AB may be used in process(y). Examples include Cl₂, Br₂, I₂, ClF, ClBr, and ICl. Preferably, atleast one of A or B is Cl and, therefore, 1243zf is chlorinated bycontacting it with Cl₂, ClF, ClBr and/or ICl. Chlorine (Cl₂) is apreferred chlorinating agent.

In this process, the zinc/chromia catalyst acts as a chlorination,fluorination and dehydrohalogenation catalyst.

Process (y) may be carried out in the liquid or vapour phase and at atemperature of from about −100 to about 400° C., such as from about 0 toabout 390° C. or about 100 to about 350° C., e.g. about 150 to about300° C. A pressure of from 0 to about 30 bara may be used in process(y), such as from about 0.1 to about 25 bara or about 0.5 to about 20bara, e.g. from about 1 to about 20 bara.

Typically, the molar ratio of 1243zf:compound of formula AB (e.g. Cl₂)in process (y) is from about 10:1 to about 1:5, such as from about 5:1to about 1:2, for example from about 3:1 to about 1.5:1 (e.g. about2.5:1 to about 1:1). The molar ratio of HF:organics is typically in therange of from about 0.1:1 to about 100:1, such as from about 0.5:1 toabout 50:1 or about 1:1 to about 40:1, e.g. from about 2:1 to about 30:1or from about 5:1 to about 20:1.

Typically, the 1234yf formed in process (y) is purified. This may beachieved by conventional methods, such as by distillation, condensation,phase separation and/or scrubbing (e.g. with water or aqueous base).

In a further embodiment, the subject invention provides a process forpreparing 3,3,3-trifluoropropene (1243zf), the process comprisingcontacting a compound of formula CX₃CH₂CH₂X or CX₃CH═CH₂, with hydrogenfluoride (HF) in the presence of a zinc/chromia catalyst, wherein each Xindependently is F, Cl, Br or I, provided that in the compound offormula CX₃CH═CH₂, at least one X is not F. Unless otherwise stated,this will be referred to hereinafter as the 1243zf preparation process(of the invention).

In a preferred embodiment, this process relates to the reaction of acompound of formula CX₃CH₂CH₂X to produce 1243zf.

The compound of formula CX₃CH₂CH₂X represents any halopropane whereinX═F, Cl, Br or I. In a preferred aspect, X═F or Cl. Examples ofcompounds of formula CX₃CH₂CH₂X include 1,1,1,3-tetrachloropropane(CCl₃CH₂CH₂Cl, 250fb), 1,1,3-trichloro-1-fluoropropane (CCl₂FCH₂CH₂Cl),1,3-dichloro-1,1-difluoropropane (CClF₂CH₂CH₂Cl),3-chloro-1,1,1-trifluoropropane (CF₃CH₂CH₂Cl, 253fb) and1,1,1,3-tetrafluoropropane (CF₃CH₂CH₂F, 254fb).

In one aspect, the compound of formula CX₃CH₂CH₂X is selected from250fb, 253fb and 254fb. In a preferred embodiment, the compound offormula CX₃CH₂CH₂X is 253fb. In a further preferred embodiment, thecompound of formula CX₃CH₂CH₂X is 254fb. In a particularly preferredembodiment, the compound of formula CX₃CH₂CH₂X is 250fb.

The compound of formula CX₃CH═CH₂ represents any halopropene whereinX═F, Cl, Br or I, provided that at least one X is not F. Preferably, Xis F or Cl (provided that at least one X is not F). Examples ofcompounds of formula CX₃CH═CH₂ include 3,3,3-trichloropropene(CCl₃CH═CH₂), 3,3-dichloro-3-fluoropropene (CCl₂FCH═CH₂) and3-chloro-3,3-difluoropropene (CClF₂CH═CH₂). In a preferred aspect, thecompound of formula CX₃CH═CH₂ represents 3,3,3-trichloropropene.

The inventors have unexpectedly found that zinc/chromia catalysts areparticularly effective for the fluorination and/or dehydrohalogenationreactions required by the 1243zf preparation process. In particular, thezinc/chromia catalysts are believed to be more active than othercatalysts, such as chromia-based catalysts. This enables the 1243zfpreparation process to be conducted using less forcing conditions (e.g.lower temperature and/or pressure) than would otherwise be necessary.

The zinc/chromia catalyst may be used in the 1243zf preparation processin an amount of from about 0.01 to about 50% by weight, such as fromabout 0.1 to about 30%, for example from about 0.5 to about 20%, basedon the combined weight of organics (e.g. compound of formula CX₃CH₂CH₂Xor CX₃CH═CH₂) and HF.

The 1243zf preparation process can be carried out in any suitableapparatus, such as a static mixer, a stirred tank reactor or a stirredvapour-liquid disengagement vessel. Preferably, the apparatus is madefrom one or more materials that are resistant to corrosion, e.g.Hastelloy® or Inconel®.

The 1243zf preparation process may be carried out batch-wise or(semi-)continuously. Preferably, the process of the invention is carriedout continuously. Typically, the 1243zf preparation process is carriedout in the vapour phase.

The process may be carried out at atmospheric, sub- or super atmosphericpressure, typically at from 0 to about 30 bara, preferably from about 1to about 20 bara.

Typically, the 1243zf preparation process of the invention is carriedout a temperature of from about 100° C. to about 500° C. (e.g. fromabout 150° C. to about 500° C. or about 100 to about 450° C.).Preferably, the process is conducted at a temperature of from about 150°C. to about 450° C., such as from about 150° C. to about 400° C., e.g.from about 200° C. to about 350° C. Lower temperatures may also be usedin the process of the invention, for example in the conversion of 250fbto 1243zf, such as from about 150° C. to about 350° C., e.g. from about150° C. to about 300° C. or from about 150° C. to about 250° C.

The 1243zf preparation process typically employs a molar ratio ofHF:organics of from about 1:1 to about 100:1, such as from about 3:1 toabout 50:1, e.g. from about 4:1 to about 30:1 or about 5:1 or 6:1 toabout 20:1 or 30:1.

The reaction time for the 1243zf preparation process generally is fromabout 1 second to about 100 hours, preferably from about 10 seconds toabout 50 hours, such as from about 1 minute to about 10 or 20 hours. Ina continuous process, typical contact times of the catalyst with thereagents is from about 1 to about 1000 seconds, such from about 1 toabout 500 seconds or about 1 to about 300 seconds or about 1 to about50, 100 or 200 seconds.

The 1243zf preparation process is particularly effective for preparing3,3,3-trifluoropropene (1243zf) by contacting 1,1,1,3-tetrachloropropane(250fb) with hydrogen fluoride (HF) in the presence of a zinc/chromiacatalyst.

250fb may be purchased from common suppliers of halogenatedhydrocarbons, such as Apollo Scientific, Stockport, UK. Alternatively,250fb may be prepared by the telomerisation of carbon tetrachloride(CCl₄) and ethylene (see, for example, J. Am. Chem. Soc. Vol. 70, p2529, 1948, which is incorporated herein by reference).

The conversion of 250fb to 1243zf typically involves fluorination anddehydrohalogenation sub-steps.

For example, 250fb may be fluorinated to produce a compound of formulaCX₃CH₂CH₂Cl (wherein X═Cl or F), as illustrated in the scheme below.1243zf may be produced by a final dehydrochlorination step of thecompound of formula CX₃CH₂CH₂Cl wherein X═F. This is illustrated belowas route (a).

Alternatively, 250fb may be dehydrochlorinated to produce3,3,3-trichloropropene, followed by step-wise fluorination to produce1243zf. This is illustrated above as route (b). Routes (a) and (b)correspond to routes (ii1) and (ii2), respectively, as described hereinin relation to step (ii) of the process of the invention.

Either or both routes (a) and (b) may be operable to convert 250fb to1243zf. For example, CCl₂FCH₂CHCl in route (a) may be dehydrochlorinatedto produce CCl₂FCH═CH₂ in route (b). It is anticipated that some ofthese reactions may occur spontaneously if HF and 250fb are mixed atelevated temperatures, but the reaction will not go to completion in theabsence of a zinc/chromia catalyst in any reasonable timescale.

Surprisingly, the inventors have found that zinc/chromia catalysts areeffective at facilitating the one-pot conversion of 250fb and HF to1243zf. In particular, the activity of the catalyst is believed to allowless forcing conditions (e.g. lower temperatures) compared to known(vapour phase) processes for producing 1243zf, whilst maintainingexcellent conversion of 250fb and selectivity to 1243zf.

The invention will now be illustrated by the following non-limitingexamples.

EXAMPLE 1 Single Stage Dehydrohalogenation of CF₃CFHCH₂F (245eb) to1234yf

A 1.25 cm (0.5″)×30 cm Inconel reactor tube loaded with 4 g 5.2%zinc/chromia catalyst. The catalyst was dried under flowing nitrogen (50ml/min) for 2 hours at 250° C. After the drying time, HF (5-8 ml/min)was introduced into the nitrogen stream to begin fluorination of thecatalyst. The temperature was ramped to 380° C. at 40° C./min and heldthere for 16 hours. After 2-3 hours HF breakthrough was detected in thereactor off-gas and the nitrogen flow was switched off. After thistreatment the reactor temperature was reduced to the temperatures shownin Table 1 and a mixture comprising nitrogen and 245eb passed over it.Samples of the reactor off-gas were taken and analysed by GC and GC-MS.The GC was calibrated using known standards to determine responsefactors and an average response factor was used to quantify unknowns.

TABLE 1 Nitrogen flow 8 ml/min, 245eb flow 2 ml/min Temperature ° C.Product 200 225 250 275 300 325 350 375 400 1234yf 0.4 0.9 2.4 17.7 40.751.8 88.8 96.4 100.0 1243zf 0.1 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 245eb99.2 97.2 93.2 71.2 59.2 48.2 2.9 0.0 0.0 245cb 0.2 1.7 4.3 11.1 0.0 0.08.2 3.6 0.0 245cb = CF₃CF₂CH₃

The results in Table 1 show that zinc/chromia is a surprisinglyeffective catalyst for the dehydrofluorination of 245eb to 1234yf.

EXAMPLE 2 Preparation of 1234yf/245eb from 243db

Two Inconel reactors (30 cm×0.5″) were loaded with 6 g each of a 5.2%Zn/chromia catalyst. These tubes were then places in series and thecatalyst dried under flowing nitrogen (80 ml/min) at 250° C. and 3 bargpressure overnight. The catalyst was then activated by treatment with amixture of 4 ml/min HF and 80 ml/min nitrogen at 300° C. and 3 bargpressure for a period of 72 hours. Whilst at 300° C. the nitrogen flowwas reduced to zero. When HF breakthrough was detected (4 hours), thetemperature was ramped to 380° C. at 25° C./hour and held there for afurther 7 hours.

After activation the pressure was increased to 15 barg and the firstreactor temperature was set to 340° C. and the second set to 100° C. anda feed mixture consisting of 243db (10 ml/min) and HF (100 ml/min)passed through them. The gases exiting the train of reactors weresampled and analysed by GC-MS, the results are presented below:

243db conversion 90

Products: 1233xf (70%), 244 isomers including CF₃CFClCH₃ (10%), 1234yf(1.4%), 245eb (1.0%)

EXAMPLE 3 Hydrofluorination of 250fb (CCl₃CH₂CH₂Cl) at Elevated Pressure

The reactor, made from an Inconnel tube 30 cm×0.5 inches, was chargedwith 6 g of a 5.2% Zn/Chromia catalyst which was essentially amorphousin character, which was treated as follows:

The catalyst was first dried by heating under nitrogen (80 ml/min) at250° C. and 3 barg for 48 hours. Next, pre-fluorination of the catalystwas begun by introducing HF (4 ml/min) into the nitrogen stream andincreasing the temperature to 300° C. for 16 hours. During the last 5hours the nitrogen flow was reduced steadily to zero. The temperaturewas then ramped to 380° C. at 25° C./hr and held at 380° C. for 7 hoursand then cooled to 250° C. at 25° C./hr.

A feed mixture comprising 250fb (3 ml/min) and HF (45 ml/min) was thenpassed over the catalyst at 15 barg and 200° C. The gases exiting thereactor were periodically sampled and analysed by GC after passingthrough an alkaline scrubber to remove acid gases. The only productsdetected in the reactor off-gases following removal of the acid gaseswere the desired product 1243zf (91 mol %, CF₃CH═CH₂) and1,1-difluoro-1,3-dichloropropane (9 mol %, CF₂ClCH₂CH₂Cl).

It is believed that the 1,1-difluoro-1,3-dichloropropane could beconverted to 1243zf by altering the reaction conditions (e.g. byincreasing the temperature and/or contact time). In this way, 250fbcould be fully converted in 100% selectivity to 1243zf in a single pass.

EXAMPLE 4 Hydrofluorination of 250fb (CCl₃CH₂CH₂Cl) at AtmosphericPressure

The reactor, made from an Inconnel tube 30 cm×0.5 inches, was loadedwith 2.0 g of a 5.2% wt Zn on chromia catalyst which was essentiallyamorphous in character. The catalyst was then dried under nitrogen (80ml/min) at 250° C. for 3 hours. HF (20 ml/min) was then introduced intothe nitrogen flow and pre-fluorination of the catalyst commenced. WhenHF was detected in the reactor off-gases the reactor temperature wasramped from 250° C. to 370° C. at 25° C./hr and maintained there for 7hours before being cooled back to 200° C. at 25° C./hr.

A feed mixture comprising 250fb (1 ml/min), HF (25 ml/min) and nitrogen(30 ml/min) was fed to the reactor at 200° C. for a total of 15 hours.The gases exiting the reactor were scrubbed with a an alkaline solutionto remove acid gases and analysed by GC-MS and GC. The only speciesidentified in the scrubbed reactor off-gases throughout the wholeexperiment was 1243zf.

Examples 3 and 4 demonstrate that the reaction of 250fb with HF using azinc/chromia catalyst selectively produces 1243zf under very mildconditions.

EXAMPLE 5 Vapour Phase Conversion of 254fb (CF₃CH₂CH₂F) to 1243zf(CF₃CH═CH₂)

The reactor, made from an Inconnel tube 30 cm×0.5 inches was loaded with2.0 g of a 5.2% wt Zn on chromia catalyst which was essentiallyamorphous in character. The catalyst was then dried under nitrogen (80ml/min) at 250° C. for 3 hours. HF (20 ml/min) was then introduced intothe nitrogen flow and pre-fluorination of the catalyst commenced. WhenHF was detected in the reactor off-gases the reactor temperature wasramped from 250° C. to 370° C. at 25° C./hr and maintained there for 7hours before being cooled back to 200° C. at 25° C./hr.

Mixtures of HF and 254fb were then fed across the catalyst at varioustemperatures and ratio's to demonstrate the conversion of 254fb to1243zf. Nitrogen carrier gas flows were used to aid delivery of thefeeds to the reactor. The gases exiting the reactor were analysed byGC-MS and GC. The results are summarised in the Table below:

Temperature (° C.) 200 225 250 200 225 250 275 300 300 225 250 254fbfeed 13.5 12.1 16.7 20.4 22.9 10.6 12.8 10.0 1.0 4.9 4.9 (ml/min) HFfeed 27.9 27.9 27.6 34.3 35.3 35.4 35.2 35.6 35.3 0 0 (ml/min) Ratio 2.12.3 1.7 1.7 1.5 3.3 2.8 3.6 35.4 N/A N/A HF:254fb Total N₂ flow 10.110.1 10.1 10.1 10.1 10.1 10.1 10.1 10.1 5 5 (ml/min) ROG* 254fb 93.350.1 14.8 93.3 71.9 17.4 1.5 0.1 0.7 1.3 0.1 (mol %) ROG* 6.7 49.9 85.26.7 28.1 82.6 98.5 99.9 99.3 98.7 99.9 1243zf (mol %) *ROG = ReactorOff-gas composition

As can be seen the conversion of 254fb to 1243xf is clean and facileover a zinc/chromia catalyst at moderate conditions.

The invention claimed is:
 1. A process for the preparation of2,3,3,3-tetrafluoropropene (1234yf) comprising: (a) contacting in thevapor phase at a temperature of from 100 to 400° C. and atsuper-atmospheric pressure up to 30bara.1,1,1-trifluoro-2,3-dichloropropane (243db) with hydrogen fluoride(HF) in the presence of a zinc/chromia catalyst containing from 0.01 toabout 25% by weight of zinc or a compound of zinc to produce a compoundhaving the formula CF₃CHFCH₂X, wherein X is Cl or F; and (b)dehydrohalogenating the compound of formula CF₃CHFCH₂X to produce1234yf, said dehydrohalogenating being (i) induced thermally, (ii)base-mediated, or (iii) catalyzed by a catalyst selected form acarbon-based catalyst, a catalyst comprising a main group metal, or acatalyst comprising a transition metal.
 2. A process according to claim1 wherein step (a) is carried out at in the vapour phase a temperatureof from 100 to 380° C. and a super-atmospheric pressure of from up to 28bara.
 3. A process according to claim 1 wherein step (b) is carried outat in the vapour and/or liquid phase a temperature of from −70 to 1000°C. and a pressure of from 0 to 30 bara.
 4. A process according to claim1 wherein step (b) is carried out in the presence of a catalyst selectedfrom the group consisting of: zinc/chromia catalyst, a crown ether,including 18-crown-6, a quaternary ammonium salt, fluorinated catalysts,and mixtures thereof.
 5. A process according to claim 4 wherein step (b)is carried out at a temperature of from −70 to 400° C.
 6. A processaccording to claim 1 wherein step (a) is carried out at a pressure offrom 5 to 28 bara.
 7. A process according to claim 1 wherein step (b) iscarried out at a pressure of from 0.1 to 20 bara.
 8. A process accordingto claim 1 wherein step (b) is carried out in the presence of HF.
 9. Aprocess according to claim 1 wherein step (b) is carried out in theabsence of an added HF feed.
 10. A process according to claim 1 whereinstep (b) is carried out in the presence of a diluent gas.
 11. A processaccording to claim 1 wherein the molar ratio of HF:organics in step (a)is from 1:1 to 100:1.
 12. A process according to claim 1 wherein themolar ratio of HF:organics in step (b) is from 0.01:1 to 50:1.
 13. Aprocess according to claim 1 wherein step (b) is carried out in thepresence of a base.
 14. A process according to claim 13 wherein step (b)is carried out at a temperature of from −50 to 300° C.
 15. A processaccording to claim 13 wherein the base is selected from a metalhydroxide, including alkali metal hydroxides, sodium hydroxide andpotassium hydroxide, an alkaline earth metal hydroxide, includingcalcium hydroxide, metal amide and mixtures thereof.
 16. A processaccording to claim 13 wherein step (b) is carried out in a solvent. 17.A process according to claim 16 wherein the solvent is selected fromwater, alcohols, diols, polyols, polar aprotic solvents and mixturesthereof.
 18. A process according to claim 17 and wherein the processoptionally is carried out in the presence of a co-solvent or diluent.19. A process according to 1 comprising the step (iii) of contacting3,3,3-trifluoropropene (1243zf) with a compound of formula AB to producea compound of formula CF₃CHACH₂B wherein A and B represent,independently, H, F, Cl, Br or I, provided that A and B are not both Hor F.
 20. A process according to claim 19 comprising the step (ii) ofconverting 1,1,1,3-tetrachloropropane (250fb) to 3,3,3-trifluoropropene(1243zf).
 21. A process according to claim 20 comprising the step (i) oftelomerising ethylene and carbon tetrachloride (CCI₄) to produce the1,1,1,3-tetrachloropropane.
 22. A process according to claim 19 whereinthe compound of formula AB is Cl₂ and the compound of formula CF₃CHACH₂Bis 1,1,1-trifluoro-2,3-dichloropropane (243db).